Polypropylene copolymers are widely used in applications where increased clarity, improved impact strength and lower heat seal temperatures are preferred. The typical comonomer used in most commercial polypropylene copolymers, also termed as Random Copolymers (RCP), is ethylene. There are many examples of other alpha olefins that have been used either instead of ethylene or in conjunction with ethylene to copolymerize with propylene. For example, WO 99/67307 discloses propylene terpolymers comprising propylene, ethylene or a C4 to C6 olefin, and a different C4 to C12 olefin. In particular, WO 99/67037 discloses examples of a propylene-butene-hexene terpolymer and a propylene-ethylene-butene terpolymer. Similarly WO 99/67094 discloses multi-layer films comprising similar polypropylene terpolymers. Examples of propylene-hexene and propylene-octene copolymers and articles made therefrom have been detailed in WO 97/19991. U.S. Pat. No. 5,658,997 describes the polymerization of propylene-ethylene, propylene-butene and propylene-octene copolymers using metallocene catalysts. Propylene-ethylene, propylene-butene and propylene-octene examples are shown. EP 1 031 584 describes a propylene copolymer comprising propylene, at least one α-olefin (2-20 carbon atoms) and a cyclic olefin. In all these cases, the polymerization involves the reaction between propylene and feeds of pure comonomer(s) that can be introduced into the reactor in controlled amounts. The purification of the desired comonomers to obtain only the desired alpha olefin is a large part of the cost of the comonomer. There is a need in the art for new, more efficient and more cost effective methods for polymerizing olefins. This invention describes the polymerization of propylene with a mixed olefin feed to yield polymers with useful properties. The use of a mixed feed reduces the cost of the comonomer feed stream without compromising any of the desirable properties of polypropylene copolymers.
Process to make polymers comprising multiple alpha-olefin monomers (ethylene, propylene and butene) have been disclosed in U.S. Pat. No. 6,417,416. Likewise WO 01/46278 discloses multiple monomer propylene based polymers produced using metallocene type catalysts. WO 99/67094 discloses polymers of propylene, butene and hexene made with metallocene type catalysts. WO 97/19991 discloses polymers of propylene and higher alpha-olefins (C5 and above), in particular WO 97/19991 discloses copolymers of propylene, a first alpha olefin (selected from pentene, 4-methyl-pentene-1, hexene or octene), and a second alpha-olefin (selected from ethylene, butene, 4-methyl-pentene-1, hexene or octene).
Other references of interest include: WO 99/67094; U.S. 2001/0000258 A1; CA 2,125,247; U.S. Pat. No. 5,658,997; WO 99/67307; U.S. Pat. No. 6,417,416; WO 99/19392; WO 99/67307; WO 01/07493; JP2000178319; EP 1 031 584; and WO 01/18109.